This application relates to the art of switches and, more particularly, to thermostatic switches. The invention is particularly applicable for use as a sensor switch in controls for gas burners and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used in other environments.
U.S. Pat. No. 3,589,846 discloses a single pole single throw thermostatic switch that is normally closed at ambient temperature. When an igniter for a gas burner is energized, radiant heat received by a bimetal in the switch eventually opens the contacts and the control circuit then opens a gas supply valve for the burner. Radiant heat from the burner maintains the bimetal at an elevated temperature to keep the contacts open. In a switch of the type described, a burner flameout can result in the undesirable continued flow of raw gas if the switch malfunctions with the contacts open. It would be desirable to have an arrangement for checking on the condition of the sensor switch.